# 蓝桥杯-危险系数

``````import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class 危险系数 {

public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner scanner = new Scanner(System.in);
int n = scanner.nextInt();
int m = scanner.nextInt();
TuNode[] tuNodes = new TuNode[n];
List<TuNode> geDian=new ArrayList<TuNode>();
int i;
for (i = 0; i < n; i++) {
tuNodes[i] = new TuNode(i + 1);
}
int x;
int y;
for (i = 0; i < m; i++) {
x = scanner.nextInt();
y = scanner.nextInt();
}
int qiDian=scanner.nextInt();
int zhongDian=scanner.nextInt();
List<TuNode> jiHe = new ArrayList<TuNode>();

List<TuNode> list =search(tuNodes[qiDian-1], tuNodes[zhongDian-1], jiHe,geDian);

if (list.size() == 0) {
System.out.println("-1");
} else {
System.out.print(geDian.size()-2);
}
}

public static List<TuNode> search(TuNode qiDian, TuNode zhongDian,
List<TuNode> jiHe,List<TuNode> geDian) {
int i;

List<TuNode> listTemp1;

List<TuNode> listTemp2 = new ArrayList<TuNode>();

List<TuNode> listTemp3 = new ArrayList<TuNode>();

for (i = 0; i < qiDian.jiedian.size(); i++) {

// 将jiHe中的元素赋给listTemp1
listTemp1 = new ArrayList<TuNode>(jiHe);

// listTemp2中添加当前循环元素

// 对listTemp2取listTemp1的交集
listTemp2.retainAll(listTemp1);

if (qiDian.jiedian.get(i).value == zhongDian.value) {

geDian.retainAll(listTemp1);

return listTemp1;
} else if (listTemp2.size() == 0) {

List<TuNode> listTemp4 = new ArrayList<TuNode>(listTemp1);

List<TuNode> listTemp5 = search(qiDian.jiedian.get(i),
zhongDian, listTemp4,geDian);
if (listTemp3.size() != 0) {
if (listTemp5.size() < listTemp3.size()
&& listTemp5.size() != 0) {
listTemp3 = new ArrayList<TuNode>(listTemp5);
}
} else {
listTemp3 = new ArrayList<TuNode>(listTemp5);
}
}
listTemp2.clear();
}
return listTemp3;
}
}

class TuNode {
int value;
List<TuNode> jiedian = new ArrayList<TuNode>();

public TuNode(int value) {
// TODO Auto-generated constructor stub
this.value = value;
}
}
``````